Preheat a grill to medium-low. In a small bowl, combine the brown sugar, garlic powder, chili powder, black pepper, salt, cayenne, oregano and thyme. Rub the spice mixture on the meaty side of the ribs and arrange, seasoned side up, in a large roasting pan; cover tightly with aluminum foil. Place on the grill and cook until the meat is fork-tender, about 1 1/2 hours.
Increase the heat to medium. Combine the olive oil and vinegar in a cup and baste the ribs with the mixture. Transfer the ribs directly to the grill grate, cover and cook, turning, until lightly charred, 5 to 10 minutes.